The invention concerns a valve actuation mechanism for an internal combustion engine on an automotive vehicle. The invention also concerns an automotive vehicle, such as a truck, equipped with such a valve actuation mechanism.
Automotive vehicles, such as trucks, often rely on an engine brake system to slow down in order, for example, to reduce wear of the friction brake pads and to prevent overheating of the friction brakes, particularly on downward slopes. It is known to perform engine brake by acting on the amount of gas present in the cylinders of the engine in two distinct phases. In a first phase, when the pistons are near a bottom dead center, one injects exhaust gases into the chambers of the cylinders so as to slow down the pistons when they move towards their high level. This is done by slightly opening at least a valve connected to an exhaust manifold, while exhaust gases are prevented to be expelled from the exhaust pipe and thereby at a certain pressure above atmospheric pressure. In the second phase, the gases which are compressed the piston are expelled from the chamber of the cylinder when the piston is at or near its top dead center position in order to prevent an acceleration of the piston under effect of volumic expansion of compressed gas. This is done by slightly opening a valve so as to expel gases from the cylinder. In most cases, the valve (or valves) which is (are) opened for the engine brake function is (are) a main exhaust valve. Such an engine brake system is described in document WO-A-9009514.
To perform these engine brake valves movements, also called engine brake valves lifts, the engine comprises, for each cylinder, a rocker acting, on the valves to open and close them. The rocker is acted upon by a rotating cam which has at least one lift sector to cause the lifting (opening) of the valve. If the valve is also an exhaust or an intake valve, the corresponding cam will comprise a main valve lift sector and one or several auxiliary valve lift sectors, also called main valve lift bump and auxiliary valve lift bump. When engine brake is needed, a cam follower surface of the rocker is moved in close contact with a cam of a camshaft moving the rocker, so that the brake movements of the valve are obtained when the cam follower interacts with the auxiliary valve lift sectors. In normal operating conditions of the engine, the valves should not perform these movements and the roller of the rocker is kept slightly remote from the cam, so that the cane follower does not interact with the auxiliary valve lift sectors. The distance or clearance between the roller and the cam ensures that only the larger main lift sector on the cam, dedicated to the main exhaust event, causes an opening of the exhaust valve, but not one or several smaller auxiliary lift sectors dedicated to the engine brake function. This clearance is suppressed when engine brake is needed, by moving an activation piston of the rocker to make a close contact between the roller and the cam, so that engine brake dedicated lift sectors on the cam also cause an opening of the valve. An engine brake system having such valve actuation mechanism is described in WO-A-91/08381.
Engine brake systems generally comprise a control valve to direct pressurized control fluid pressure in a chamber adjacent to the piston to move the activation piston from its initial position to its engine brake actuation position. The control valve controls whether or not the engine brake function is activated. This control valve lets pressurized, control fluid flow, at a pressure of for example 2 to 5 bars, towards each rocker as long as the engine brake function is needed, which typically lasts several seconds or tens of seconds during which the engine and the cam shaft may perform several hundreds or thousands of complete revolutions.
Some know systems comprise, in the rocker, a controlled blocking valve comprising a regular ball check valve, for effectively blocking fluid flow in the direction from the piston chamber to the fluid feeding circuit, and a state switching piston which is spring braised towards a position where it pushes the ball of the ball check valve off its seat. The blocking valve as whole is thereby in an open state. When a certain pressure is delivered by the control valve, the pressure pushes the state switching piston to a retracted position, which allows the ball check valve to operate conventionally. The blocking valve as a whole is then in a blocking state. The state switching piston is located upstream of the ball valve, so that when the ball valve is closed, it is controlled by a pressure which is the pressure delivered by the control valve, which pressure may different than the pressure in the piston chamber. Such systems require a quite complex design of the blocking valve.
In U.S. Pat. No. 6,450,144, various designs of a controlled blocking valve are provided to prevent or limit fluid flow out of the chamber when the piston is in its engine brake actuation position. This blocking valve is permanently controlled using a control pressure coming from the upstream portion of the fluid circuit leading to the blocking valve.
It is desirable to propose a new valve actuation mechanism for an automotive vehicle, in which the blocking valve is simpler in design.
To this end, the invention concerns, according to an aspect thereof, a valve actuation mechanism for an internal combustion engine on an automotive vehicle, comprising at least one rocker adapted to exert a valve opening force on at least a portion of an opening actuator for opening a cylinder valve, via an activation piston of the rocker movable in a piston chamber of the rocker under action of a fluid pressure raise in the piston chamber, from a first position, in which an engine operating function is deactivated, to a second position, in which said engine operating, function is performed, the rocker comprising a controlled blocking valve having an open state allowing bidirectional fluid flow between a fluid feeding circuit of the rocker and the piston chamber, and as blocking state to block, fluid flow from the piston chamber to the fluid feeding circuit to block the activation piston is in its second position, wherein the control of the blocking valve between its open state and its blocking state is performed by action of a force exerted by the fluid pressure in the piston chamber on a valve member of the blocking valve which is exposed to the fluid pressure in the piston chamber.
According to further aspects of the invention which are advantageous but not compulsory, such a valve actuation mechanism can incorporate one or several of the following features:                The controlled blocking valve comprises a single unitary moveable valve member, which controls both the state of the blocking valve and the effective fluid flow from the piston chamber to the fluid feeding circuit.        The valve member is exposed to the fluid pressure in such a way that, at least when the valve member is in a first position allowing bidirectional fluid flow through the blocking valve, the resulting force of the fluid pressure on the valve member tends to move the valve member towards a second position blocking fluid flow to the fluid feeding circuit through the blocking valve.        The area of surfaces of the valve member which are exposed to the fluid pressure are dimensioned so that, at least when the valve member is in the first position, the resulting force of the fluid pressure on the valve member tends to move the valve member towards its second position.        The valve member is movable in a valve chamber which is in fluidic communication with the chamber of the activation piston and with a main fluid feeding duct.        The first position of the valve member corresponds to the open state of the controlled blocking valve, in which the main fluid feeding duct is fluidly connected to the piston chamber, and the second position of the valve member corresponds to the blocking state of the controlled blocking valve, in which the main fluid feeding duct and the piston chamber are fluidly disconnected.        The valve member defines in the valve chamber a fluid pressure compartment which is permanently fluidly connected to the piston chamber so as to be permanently at the same pressure as the piston chamber.        The valve chamber and the valve member are designed so that the area of surfaces of the valve member which are exposed to the fluid pressure in the fluid pressure compartment are dimensioned so that, at least when the valve member is in the first position, the resulting force of the fluid pressure on the valve member tends to move the valve member towards its second position.        When the valve member is in its second position, the fluid pressure compartment and the piston chamber are fluidly disconnected from the main fluid feeding duct.        When the valve member is in its second position, the fluid pressure in the main fluid feeding duct is applied on a snake of the valve member which is substantially perpendicular to the movement of the valve member, so that the resulting effort of the action of the fluid pressure in the main feeding duct on the valve member does not tend to cause any substantial movement of the valve member.        The valve chamber and the valve member define a valve seat where the valve chamber and the valve member are in contact with each other in the second position of the valve member so as to fluidly disconnect the piston chamber and the fluid pressure compartment from the main fluid feeding duct, and whereas, when the valve member is in its first position, the valve member and the valve chamber are separated at the valve seat so as to allow fluid communication between the piston chamber and the fluid pressure compartment and the main fluid feeding duct.        The valve actuation mechanism comprises resilient means to urge the valve member towards its first position.        The means to urge the valve member towards its first position comprise a spring exerting a force along a direction of movement of the valve member.        The valve member moves from its first position to its second position when the resulting fluid pressure force exerted on the spool exceeds the force exerted by the spring.        The valve comprises at least one communication passage which is selectively fluidly connected or not with the main fluid feeding duct depending on the position of the valve member and wherein, when the valve member is in its first position, fluid and/or fluid pressure is circulated/transmitted between the main fluid feeding duct and the piston chamber through said at least one communication passage.        The valve member comprises a peripheral surface by which it is guided in the valve chamber by being in contact with a corresponding internal surface of the valve chamber, wherein said main fluid feeding duct arrives in said inner surface and wherein the valve member comprises a peripheral groove forming a volume in fluidic communication with the communication passage, wherein said peripheral groove is in fluidic communication with the main fluid feeding duct when the valve member is in its first position, and wherein said peripheral groove faces an internal wall surface of the valve chamber when the valve member is in its second position.        The communication passage is a duct extending through the valve member along a longitudinal axis of the valve member and which is in fluidic communication with the peripheral grove thanks to several ducts distributed around the communication duct.        The valve member comprises a plurality of communication grooves provided on an outer peripheral surface of the valve member.        The valve member comprises at least one obtruding member adapted to obtrude at least one on connected to the main fluid feeding duct when the valve member is in its second position.        An outer surface of the valve member comprises slots which face the main fluid feeding duct when the valve member is in its first position and which face an internal wall of the valve chamber when the valve member is in its second position.        The communication passage is a duct extending through the valve member along the longitudinal axis of the valve member and wherein an obtruding member protruding from a surface of the valve chamber obtrudes said communication duct when the valve member is in its second position.        The valve member is a spool adapted to translate along a longitudinal axis of the valve chamber.        The rocker is moved by a camshaft and, in the second position of the activation piston, a cam follower of the rocker is adapted to read at least one auxiliary valve lift sector of a cam of the camshaft so as to perform said engine operating function.        
The invention also concerns an automotive vehicle, such as a truck, comprising a valve actuation mechanism as mentioned here-above.